1. Field of the Invention
This invention relates generally to control apparatus and more particularly to apparatus for controlling a plurality of devices coupled to a two conductor power line.
2. Discussion of the Related Art
It is known in the related art to control electrical devices with a plurality of control lines that are coupled to the devices in addition to the power lines. The control lines transmit information to the electrical devices relating to activation and interruption of activity and return sensor information from the devices being controlled. However, the use of a multiplicity of control lines can be increasingly complicated for any but a minimum number of devices, and each control line increases the possibility that a malfunction will occur during the interconnection of the control lines to the respective devices. It is also known in the related art to provide a carrier signal that can be applied to the power line. Modulation can be superimposed on the carrier signal, and when demodulation apparatus is available in the vicinity of the electrical devices, control information can be transfered via the carrier frequency.
A need has therefore been felt for control apparatus that would minimize or completely eliminate the use of independent control lines or imposed carrier signals and would transfer information between the power source and the operating device by means of the power lines with a minimum of additional apparatus.